I am trying to optimize a utility which groups an incoming stream into (currently) six groups, based on the first two letters. What I have now looks like: 
my @Group1 = qw( H0 K0 PA PB PC PD PE PF PG PH ); #etc
my @Group2 = qw( PX PY PZ P1 P2 P3 P4 P5 P6 P7 ); #etc
# etc, 6 lists defined, with 100-200 prefixes each

foreach my $code (@Group1) { $G1_Hash{$code} = 1; }
foreach my $code (@Group2) { $G2_Hash{$code} = 1; }

while (my $input = <STDIN>) {
    chomp ($input);
    my $prefix = substr($input,0,2);

    push (@G1_out, $input) if $G1_Hash{$prefix};
    push (@G2_out, $input) if $G2_Hash{$prefix};
}

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I know there has to be a more efficient solution to this. Maybe a way to define the hash in one step, instead of populating the list first?

In reply to Efficient Grouping by meetraz

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